Vehicles and other application scenarios use cameras which are placed in such a way that they are able to detect the head and eyes of a user, such as a driver of the vehicle. The basic positioning of the camera makes it possible to ascertain a gaze direction of the user. However, an absolute determination of the gaze direction with the aid of only a single camera requires a prior calibration of the camera and the gaze direction detection.
For example, the camera is calibrated using what is known as an end of line calibration (EOL calibration).
German Patent Application No. DE 10 2005 047160 uses an ellipsis identification for ascertaining the gaze direction. An exact position of the elliptical image of the circular pupilla can be utilized for inferring the position of the eye, and from that, the gaze direction of a user.
In ‘Calibration-Free Eye Tracking by Reconstruction of the Pupil Ellipse in 3-D Space, ETRA'08, 2008’, S. Kohlbecher et al. describe a stereo-based method without calibration.
Another calibration possibility consists of letting the user interact with the further element in that, for instance, the user is asked to track markers on a screen with his eyes, the marker's spatial positioning in relation to the camera being known and basically non-variable.
Each change in position of the marker on the screen results in a change in the viewer's gaze direction, which is ascertainable in camera images, at least in relative terms. The change in position of the marker, the fixed spatial-geometric relationship of the screen to the camera, and the detected relative change in the gaze direction in turn make it possible to ascertain an absolute gaze direction, possibly with the aid of camera parameters of the camera.
The use of multiple absolute gaze directions thereby makes it possible to achieve a stable calibration of the gaze direction detection.